Imagine having a Swiss Army Knife, a Multitool, a full set of a home toolbox, and a handful of other minitools all housed inside your arm. They all face different directions, some have to be rotated to access the useful bits, spun around, unfolded, then moved from an internal housing to deploy and, in all likelihood, your hand retracts back and out of the way so that the tool can be extended into that place. The thing is in constant motion as new tools are needed, whirring and rotating and retracting or extending, There're several other examples of how it looks, but for the life of me I can't remember a dang link for any of them at the moment. Gah. Up too early.
But, yeah, the thing's always whirring around as you bring out different tools for different applications, as opposed to just being a hole where you stick a bunch of tools like a closet in your arm. It's active and cyberneticly linked to your brain, so it always pushes out the tool you want.